libcamera: v4l2_controls: Cache query control information

Cache the V4L2 control info retrieved with VIDIOC_QUERY_EXT_CTRL
at control listing time for later use.

Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>

src/libcamera/include/v4l2_device.h

@@ -48,6 +48,7 @@ private:
 			    const struct v4l2_ext_control *v4l2Ctrls,
 			    unsigned int count);
 
+	std::map<unsigned int, struct v4l2_query_ext_ctrl> controlInfo_;
 	std::vector<std::unique_ptr<V4L2ControlId>> controlIds_;
 	ControlInfoMap controls_;
 	std::string deviceNode_;

src/libcamera/v4l2_device.cpp

@@ -381,6 +381,8 @@ void V4L2Device::listControls()
 		}
 
 		controlIds_.emplace_back(std::make_unique<V4L2ControlId>(ctrl));
+		controlInfo_.emplace(ctrl.id, ctrl);
+
 		ctrls.emplace(controlIds_.back().get(), V4L2ControlInfo(ctrl));
 	}